Knee Extensor Muscle Damage Protective Effect By Different Resistance Exercise Modes In Older Men

Tseng et al. (MSSE 2020) showed that the progressive elbow flexor (EF) eccentric exercise training (ET) performed once a week for 5 weeks increased maximal voluntary isometric contraction (MVC-ISO) strength and upper arm circumference (CIR), and attenuated the extent of muscle damage after maximal eccentric exercise (MaxEC) performed 7-day after the last ET in young sedentary men. However, it is not known whether this is also the case for other muscles (e.g. knee extensors: KE) and older individuals. PURPOSE: This study compared training and muscle damage protective effects between ET, concentric (CT) and isometric exercise training (IT) of the KE performed by older men. METHODS: Healthy older men (60-76 y) were placed to either ET, CT, IT or a control group (n = 12/group). ET and CT groups performed 30-60 eccentric-only and concentric-only contractions of the KE, respectively, once a week for 12 weeks while progressively increasing the intensity. IT group performed 30 MVC-ISO of the KE at a long muscle length, and control group did not perform any training. At one week after the last training session, all participants performed 60 MaxEC of the KE. MVC-ISO, CIR, and rectus femoris muscle thickness (MT) were measured before and 4-day after the training, and muscle damage markers (e.g., MVC-ISO, muscle soreness and plasma creatine kinase activity: CK) were measured before and for 5-day post-MaxEC. Changes in the measures were compared between the four groups by a mixed-design two-way ANOVA. RESULTS: ET increased MVC-ISO, CIR and MT (30 ± 6%, 1.3 ± 0.2%, 4.0 ± 1.4%) greater (P < 0.05) than CT (16 ± 4%, 0.5 ± 0.1%, 2.0 ± 1.1%) and IT (20 ± 3%, 0.8 ± 0.3%, 3.0 ± 1.1%), and the increases were greater (P < 0.05) after IT than CT, without increases for the control group. Changes in muscle damage markers (e.g., MVC-ISO at 2-day post-MaxEC, peak muscle soreness and CK) were smaller (P < 0.05) for ET (-2 ± 1%, 2 ± 4 mm, 206 ± 34 IU/L) than CT (-21 ± 7%, 15 ± 14 mm, 1157 ± 493 IU/L), IT (-15 ± 7%, 8 ± 9 mm, 691 ± 288 IU/L) and control (-26 ± 3%, 22 ± 10 mm, 1478 ± 1004 IU/L). The changes were smaller (P < 0.05) for IT than CT, and CT than control group. CONCLUSION: These results suggest that ET induced greatest muscle adaptations and damage protective effect in older adults. Thus, including eccentric contractions in resistance exercise training is also important for older individuals.